1. Field of the Invention
This invention relates to a method of measuring a surface geometry of a sample using a scanning probe microscope and an apparatus therefor, and more particularly to a measuring method with and apparatus of a scanning probe microscope adapted to measure a surface geometry of a sample by vibrating the sample.
2. Background Information
There is known a measuring method, as a conventional measuring method for measuring a surface geometry of a sample by using a scanning probe microscope, wherein a cantilever is resonantly vibrated to lightly tap a sample surface and the cantilever is feedback-controlled in Z directional position (distance between the sample and the cantilever) by a servo system so as to bring constant the state of tapping, thereby obtaining geometry data on the sample surface. This method is generally referred to as a tapping mode.
According to this measuring method, there possesses a merit that the Q value of cantilever resonant frequency, at a resonant frequency f0, becomes approximately 100-300 and large amplitude of vibration is obtainable even if the cantilever is vibrated by an oscillator with small amplitude output.
However, in the above conventional measuring method the resonant frequency f0 and the resonant frequency Q value vary for each cantilever. There has been a problem that, if the cantilever is exchanged, time is required for adjustment until starting a sample surface measurement and further the adjustment necessitates experience. In particular, if the Q value changes, the amplitude of cantilever vibration varies. Accordingly, there has been a problem that there is difficulty in causing the cantilever to perform Z rough movement to a position at which a needle tip of the cantilever lightly tap the sample surface. Also, there has been a problem that, although the needle tip urging pressure against the sample surface varies between a shallow Z rough movement case and a deep case, the change of urging pressure causes the sample surface detection data to vary thus resulting in variation in observation image on the same sample.
It is an object of the present invention to eliminate the above-stated problems in the conventional art and provide a measuring method with and apparatus of a scanning probe microscope which, even if the cantilever is exchanged, can easily initially set constant at all times the pressure that a needle tip of a cantilever taps a sample surface.
Also, it is another object to provide a measuring method with and apparatus of a scanning probe microscope by which, even if the cantilever is exchanged, variation-free and stable detection for the sample surface data can be obtained.
In order to achieve the above-described object, the present invention is a scanning probe microscope measuring method of measuring a geometry of a surface of a sample by contacting a cantilever with the surface of the sample, the scanning probe microscope measuring method characterized in that: the geometry of the sample surface is measured while putting the cantilever in light contact with the sample surface in a state that the sample is being vibrated at a frequency that is substantially free of affection of resonant frequencies inherent to the cantilever and the sample.
The vibrational frequency of the sample may be a new resonant frequency of the cantilever shifted by contacting the cantilever with the sample. Also, the vibrational frequency of the sample may be a resonant frequency caused by contacting the cantilever with the sample.
Also, according to the present invention, in a scanning probe microscope for measuring a surface of a sample, a structure is proposed that has: an oscillator which can output an electric signal at a frequency that is substantially free of affection of resonant frequencies inherent to the cantilever and the sample; a Z servo system for feedback-control on vertical movement of the cantilever; a vibrator for responding to an output signal of the oscillator and an output signal of the Z servo system, to vibrate the sample at a frequency that is substantially free of affection of resonant frequencies inherent to the cantilever and the sample; wherein the Z servo system holds equilibrium at a point where a contact pressure of the cantilever against the sample becomes a predetermined magnitude.
Furthermore, a scanning probe microscope according to the present invention may be, in the above structure, structured that the sample is vibrated at a resonant frequency caused by contacting the cantilever with the sample.
Also, according to the present invention, in a scanning probe microscope of measuring a geometry of a surface of a sample by contacting a cantilever with the surface of the sample, a structure is proposed that has: an oscillator which can output an electric signal of a new resonant frequency of the cantilever shifted by contacting the cantilever with the sample; a Z servo system for feedback-control on vertical movement of the cantilever; a vibrator for responding to an output signal of the oscillator and an output signal of the Z servo system, to vibrate the sample at the new resonant frequency; wherein the Z servo system holds equilibrium at a point where a contact pressure of the cantilever against the sample becomes a predetermined magnitude.
According to the method of the present invention, because the sample is vibrated by avoiding the resonant frequencies inherent to the cantilever and the sample, the measuring manner becomes simple as compared with the conventional measuring method in the tapping mode. Also, even if the cantilever is exchanged, it becomes possible to obtain constant observation images at all times.
In this case, it is possible to structure with using a resonant frequency newly caused when the cantilever comes into contact with the sample regardless of free vibration of the cantilever and the sample as single members. This can enhance sensitivity of measurement. Also, by vibrating at a new resonant frequency of the cantilever shifted due to contacting the cantilever with the sample, even if the cantilever possesses two or more resonant frequencies, measurement is possible provided that the resonant frequency caused by coupling between the sample and the probe needle lies at an intermediate between them.
In any case, because the sample is put in vibration and the cantilever is contacted with this, the vibrational amplitude of the cantilever tends to increase as the cantilever approaches the sample. Due to this, it is possible to increase detection sensitivity. In this manner, because of a detection method that the vibrational amplitude becomes maximum where the probe needle extremely approaches the sample in a manner different from the tapping mode, the S/N ratio of the detection signal improves where the probe needle extremely approaches the sample, thus stabilizing detection characteristics.
Also, according to the apparatus of the present invention, because the Z servo system holds equilibrium at a point where the contact pressure of the cantilever against the sample becomes a predetermined magnitude, the initial setting for measurement (Z rough movement) becomes easy to perform. The scanning probe microscope can be easily handled by one who is not skillful.